We will determine the sites, developmental stages and mechanisms of B cell tolerance, concentrating on tolerance to those self-antigens that are the targets of disease-associated autoantibodies. The autoantibodies of interest are those that arise spontaneously in systemic autoimmune disease and include anti-dsDNA, anti-ssDNA, anti-Sm and RF. To enhance our ability to study the regulation of B cells expressing these autoantibodies, we will determine whether regulation is manifested by deletion, anergy or receptor editing; the stage B cell development or differentiation at which regulation takes place; and the mechanism by which regulation is carried out. These objectives can be achieved with a new mouse model, site directed transgenics. Here variable region genes coding for autoantibodies are introduced into their normal genomic context. These variable region genes are subject to the normal processes and regulatory elements of antibody genes, and they lead to highly enriched populations of autoreactive B-cells. How normal mice recognize and regulate these populations can be readily studied. Our ultimate goal is to know why normal mechanisms of B-cell tolerance fail in autoimmune disease. Comparison of transgene regulation in autoimmune and non-autoimmune strains of mice will identify what forms of regulation are defective and the stage(s) at which the defect is manifested. Knowing why these prominent autoantibodies are deregulated will provide a comprehensive understanding of loss of self-tolerance in systemic autoimmunity. The detailed understanding of how self-antigens interact with each of these autoantibodies will direct approaches for restoring regulation in autoimmune disease.